#surfacetension — Public Fediverse posts

Marangoni Effect in Biology

For decades, biologists have focused on genetics as the key determiner for biological processes, but genetic signals alone do not explain every process. Instead, researchers are beginning to see an interplay between genetics and mechanics as key to what goes on in living bodies.

For example, scientists have long tried to unravel how an undifferentiated blob of cells develops a clear head-to-tail axis that then defines the growing organism. Researchers have found that, rather than being guided purely by genetic signals, this stage relies on mechanical forces–specifically, the Marangoni effect.

The image above shows a mouse gastruloid, a bundle of stem cells that mimic embryo growth. As they develop, cells flow up the sides of the gastruloid, with a returning downward flow down the center. This is the same flow that happens in a droplet with higher surface tension in one region; the Marangoni effect pulls fluid from the lower surface tension region to the higher one, with a returning flow that completes the recirculation circuit.

The same thing, it turns out, happens in the gastruloid. Genes in the cells trigger a higher concentration of proteins in one region of the bundle, creating a lower surface tension that causes tissue to flow away, helping define the head-to-tail axis. (Image credit: S. Tlili/CNRS; research credit: S. Gsell et al.; via Wired)

Marangoni Bursting With Surfactants

A few years ago, researchers described how an alcohol-water droplet atop an oil bath could pull itself apart through surface tension forces. Dubbed Marangoni bursting, this phenomena has shown up several times since. Here, researchers explore a twist on the behavior by adding surfactants to see how they affect the bursting phenomenon. (Video and image credit: K. Wu and H. Stone; via GFM)

#flowVisualization #fluidDynamics #instability #MarangoniBursting #physics #science #surfaceTension #surfactant

Dancing Metal Droplets

Droplets of a gallium alloy are liquid at room temperature. When spiked with aluminum grains and immersed in a solution of NaOH, the droplets change shape and move in a random fashion. This video delves into the phenomenon, describing how a chemical reaction with the aluminum grains changes the local surface tension and creates Marangoni flows that make the droplets move. To get the droplet motion, you need to have the aluminum concentration just right. With too little, there’s not enough Marangoni flow. With too much, the hydrogen gas produced in the chemical reaction disrupts the droplet motion. (Video and image credit: N. Kim)

https://www.youtube.com/watch?v=XYRj0Ty9udo

#2024gofm #chemistry #droplets #fluidDynamics #marangoniEffect #physics #science #surfaceTension

Within a Drop

In this macro video, various chemical reactions swirl inside a single dangling droplet. Despite its tiny size, quite a lot can go on in a drop like this. Both the injection of chemicals and the chemical reactions themselves can cause the flows we see here. Surface tension variations and capillary waves on the exterior of the drop can play a role, too. Just because a flow is tiny doesn’t mean it’s simple. (Video and image credit: B. Pleyer; via Nikon Small World in Motion)

#chemistry #droplets #flowVisualization #fluidDynamics #fluidsAsArt #marangoniEffect #physics #science #surfaceTension

Active Cheerios Self-Propel

The interface where air and water meet is a special world of surface-tension-mediated interactions. Cereal lovers are well-aware of the Cheerios effect, where lightweight O’s tend to attract one another, courtesy of their matching menisci. And those who have played with soap boats know that a gradient in surface tension causes flow. Today’s pre-print study combines these two effects to create self-propelling particle assemblies.

The team 3D-printed particles that are a couple centimeters across and resemble a cone stuck atop a hockey puck. The lower disk area is hollow, trapping air to make the particle buoyant. The cone serves as a fuel tank, which the researchers filled with ethanol (and, in some cases, some fluorescent dye to visualize the flow). Like soap, ethanol’s lower surface tension disrupts the water’s interface and triggers a flow that pulls the particle toward areas with higher surface tension. But, unlike soap, ethanol evaporates, effectively restoring the interface’s higher surface tension over time.

With multiple self-propelling particles on the interface, the researchers observed a rich series of interactions. Without their fuel, the Cheerios effect attracted particles to each other. But with ethanol slowly leaking out their sides, the particles repelled each other. As the ethanol ran out and evaporated, the particles would again attract. By tweaking the number and position of fuel outlets on a particle, the researchers found they could tune the particles’ attractions and motility. In addition to helping robots move and organize, their findings also make for a fun educational project. There’s a lot of room for students to play with different 3D-printed designs and fuel concentrations to make their own self-propelled particles. (Research and image credit: J. Wilt et al.; via Ars Technica)

#3DPrinting #CheeriosEffect #DIYFluids #evaporation #flowVisualization #fluidDynamics #marangoniEffect #physics #science #surfaceTension